diff --git a/src/NXP/Classes/Tokenizer.php b/src/NXP/Classes/Tokenizer.php
index af041c1..a74bff6 100644
--- a/src/NXP/Classes/Tokenizer.php
+++ b/src/NXP/Classes/Tokenizer.php
@@ -124,6 +124,8 @@ public function tokenize() : self
                     continue 2;
 
                 case ' ' == $ch || "\n" == $ch || "\r" == $ch || "\t" == $ch:
+                    $this->emptyNumberBufferAsLiteral();
+                    $this->emptyStrBufferAsVariable();
                     $this->tokens[] = new Token(Token::Space, '');
 
                     continue 2;
diff --git a/tests/MathTest.php b/tests/MathTest.php
index e68fdb8..7af7c59 100644
--- a/tests/MathTest.php
+++ b/tests/MathTest.php
@@ -26,7 +26,7 @@ class MathTest extends TestCase
     /**
      * @dataProvider providerExpressions
      */
-    public function testCalculating($expression) : void
+    public function testCalculating(string $expression) : void
     {
         $calculator = new MathExecutor();
 
@@ -250,18 +250,47 @@ public function providerExpressions()
         ];
     }
 
-    public function testUnknownFunctionException() : void
+    /**
+     * @dataProvider incorrectExpressions
+     */
+    public function testIncorrectExpressionException(string $expression) : void
     {
         $calculator = new MathExecutor();
-        $this->expectException(UnknownFunctionException::class);
-        $calculator->execute('1 * fred("wilma") + 3');
+        $calculator->setVars(['a' => 12, 'b' => 24]);
+        $this->expectException(IncorrectExpressionException::class);
+        $calculator->execute($expression);
+    }
+
+    /**
+     * Incorrect Expressions data provider
+     *
+     * These expressions should not pass validation
+     */
+    public function incorrectExpressions()
+    {
+        return [
+          ['1 * + '],
+          [' 2 3'],
+          ['2 3 '],
+          [' 2 4 3 '],
+          ['$a $b'],
+          ['$a [3, 4, 5]'],
+          ['$a (3 + 4)'],
+          ['$a "string"'],
+          ['5 "string"'],
+          ['"string" $a'],
+          ['$a round(12.345)'],
+          ['round(12.345) $a'],
+          ['4 round(12.345)'],
+          ['round(12.345) 4'],
+        ];
     }
 
-    public function testIncorrectExpressionException() : void
+    public function testUnknownFunctionException() : void
     {
         $calculator = new MathExecutor();
-        $this->expectException(IncorrectExpressionException::class);
-        $calculator->execute('1 * + ');
+        $this->expectException(UnknownFunctionException::class);
+        $calculator->execute('1 * fred("wilma") + 3');
     }
 
     public function testZeroDivision() : void